CHARGE TRANSFER ACROSS INTERFACES OF BIOLOGICAL SYSTEMS

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The properties of the lipid bilayer-water interface will be studied by observing the kinetics of photo-generated charge transfer across the interface, of ensuing reverse reaction at that interface and of transmembrane movement of products. Electrical measurements directly probe the charge transfer with subnanosecond time resolution and angstrom (Debye length) distance from the surface. The unique ability of photoreactions to transfer this charge in sub-nanosecond times allows the study of an unprecedented time range, some ten orders of magnitude. The study will be aimed at obtaining information on the electrical and other potentials at the interface, on the molecular motion or viscosity of the interface and on the relaxation of ion atmospheres at these charged interfaces. This information is obtained by detailed analysis of the kinetics of reactions with differently charged or polar lipids and a variety of charged or polar reactants. The transit time of charged species across bilayers will be directly measured in attempts to resolve discrepancies in the literature. These measurements will be applied to the study of charge transfer in modified membrane ion channels, in bacteriorhodopsin and in photosynthetic reaction centers. The aim will be to understand the molecular determinants of the charge transfer by direct measure of the charge movements. New methodologies to measure the thermodynamic properties via kinetically resolved heat formation of photochemical cycles such as occur in phototransduction in rhodopsin, bacteriorhodopsin and photosynthetic reaction centers will be developed. They will be the extension of photoacoustic methodology to the nanosecond time range and the use of a novel method based on changes in ionic conductivity.